Genetics Lecture Notes Chs 13, 14, 15 Ch 13 I. Mendel’s Laws A. Monohybrid cross results led to the law of segregation – 1. Diploid cells have pairs of genes on homologous chromosomes. 2. The two genes of a pair separate from each other during meiosis so they end up in different gametes. B. Dihybrid cross results led to the law of independent assortment 1. Paired genes on homologous chromosomes tend to sort into gametes independently of other gene pairs during meiosis. 2. Crossovers can breakup linkage groups C. Autosomal Dominant Pattern: Trait it specifies appears in everyone who carries it – both sexes with equal frequency. Appears in every generation D. Autosomal Recessive Pattern: Trait it specifies appears only in homozygous people. Equally in both sexes, but can skip generations II. Other Inheritance Patterns A. Incomplete Dominance – phenotype of heterozygous individuals is an intermediate blend of 2 homozygous phenotypes B. Codominant – heterozygous individuals have both homozygous phenotypes, may use multiple allele systems (blood typing – ABO) C. Epistasis – 2 or more genes affect the same trait: pigments in skin and fur D. Pleiotropic – gene which affects 2 or more traits: Marfan Sydrome E. Continuous variation – range of small increments of phenotype due to multiple gene influences. 1. Generally makes bell shaped curve: human height, face length in dogs 2. Short Tandem repeats: spontaneously expand or contract quickly creating multiple alleles (longer repeats = longer doggy faces) F. X-Linked Pattern – Occurs on X chromosome 1. 2. 3. 4. Recessive pattern: X has different genetic information than Y More often in men (XY) : Baldness Carrier women: Dominant normal allele that masks recessive allele Males can pass on trait to daughters but not sons III. External influences: Nature vs. Nurture A. Environmental factors can alter gene expression by way of cell signaling pathways that ultimately affect gene controls. B. Change in Methylation (adding/removing methyl groups from regions of DNA) may enhance or suppress gene expression C. Genotype + Environment - Phenotype D. Seasonal changes in coat color, altitude and plant height, reproduction and water fleas, psychiatric disorders (ADHD) IV. Pedigrees A. Tracks inheritance patterns in families B. Genetic abnormality is an uncommon version of a heritable trait that does not result in medical problems C. Genetic disorder is heritable condition that sooner or later results in mild or severe medical problems D. Used for to visualize inheritance patterns that can be predictably associated with specific phenotypes V. Chromosomal Number A. Karyotypes are pictures of total numbers of chromosomes in an individual B. Aneuploid individuals have too many or too few copies of a chromosome C. In humans, most are lethal <1% individuals D. Nondisjunction occurs during meiosis due to faulty separating of chromosomes or chromatids in Anaphase 1 or 2. E. EX: Downs syndrome (trisomy 21), Changes in #s of sex chromosomes VI. Chromosomal Structure A. During Prophase I, faulty crossovers can result in abnormal chromosomal structure B. Changes can be harmful or lethal. Some affect fertility – ½ of all miscarriages are due to chromosome abnormalities C. Changes have accumulated in chromosomes of all species over time 1. Telomere section found in middle of Chromosome 2 of humans suspected fusing of 2 chromosomes (2A and 2B in chimpanzees) D. X and Y chromosomes were once homologous autosomes in reptilelike ancestors of mammals. 1. SRY gene mutated resulting in reduced crossing over – allowing chromosomes to diverge and mutations accumulate separately VII. DNA Cloning A. Restriction enzymes are used to cut a sample of DNA into pieces. B. DNA ligase splices the fragments into plasmids (circular pieces of DNA from bacteria). C. New recombinant DNA are inserted into host cells like bacteria D. Division of host cells produces huge populations of genetically identical cells – clones – each containing the DNA fragment E. Reverse transcriptase is used to transcribe RNA into cDNA for cloning VIII. Genetic engineering A. Scientists use a DNA library containing different fragments of DNA to represent an organism’s entire genome. B. PCR uses primers to rapidly increase number of copies of a targeted section of DNA without needing to clone living cells C. Electrophoresis – separates fragments of DNA cut by restriction by length into bands D. Sequencing reveals the order of nucleotides in DNA E. Human genome project has sequenced the entirety of the human genome (3 billion nucleotides) F. Genomics provides insights into the function of the human genome. 1. Looks for similarities between different organisms for evidence of evolutionary relationships G. DNA profiling can identify a person by SNPs (single nucleotide polymorphisms) which is an array of short tandem repeats : DNA fingerprint H. Taking one gene from one species and inserting it into an individual of a different species OR modifying it and inserting it into the same species creates GMOs. 1. 2. value Bacteria and yeast produce proteins with medical value Transgenic crops: corn and soy: pesticide resistant/increased nutritional I. Gene therapy transfers a gene into body cells to correct a genetic defect or treat disease 1. Potential benefits weigh against risks like eugenics